Variable cylinder capacity engine

ABSTRACT

A mechanical transmission device for a variable cylinder capacity engine includes at least a cylinder ( 10 ) wherein moves a piston ( 2 ), which is integral in its lower portion with a transmission member ( 3 ) co-operating through a small-sized rack ( 37 ) with a roller bearing guide device ( 4 ) and through another large-sized rack ( 35 ) with a sprocket wheel ( 5 ) linked to a connecting rod ( 6 ), a control member ( 7 ) having a large-sized rack ( 73 ) co-operating with the sprocket wheel ( 5 ), elements for fixing ( 24, 31 ) the piston ( 2 ) on the transmission member ( 3 ) which provide a preload for clamping it and ensure its centring, linking elements ( 11, 12; 71, 72 ) for rigidifying the transmission ( 3 ) and control ( 7 ) members and for increasing the flexural strength of the teeth of the large-sized racks ( 35, 73 ) and elements for lightening ( 56 ) the sprocket wheel ( 5 ) which maintain its rigidity and load capacity.

BACKGROUND OF THE INVENTION

The present invention relates to a mechanical transmission device forguiding the piston or pistons of a variable cylinder capacity engine.

The mechanical transmission device according to the present inventionimproves upon the transmission device described and protected in Frenchpatent application No. 98 15089 belonging to the Applicant.

Specifically, the transmission device described in patent No. 98 15089solved problems associated with the weight, rigidity and load-bearingcapability of the various components. This patent also solved problemsrelated to risks of the piston becoming seized in the cylinder and thevertical compactness of the engine as a whole.

SUMMARY OF THE INVENTION

The mechanical transmission device according to the present inventionproposes solutions for lightening the racks and the toothed wheel whileat the same time preserving their rigidity. The device also improves theguidance and fixing of the piston and reduces the vertical bulk of themechanical transmission device.

The mechanical transmission device according to the present inventionaddresses the risks of seizure of the piston by, on the one hand,guiding said piston in its cylinder and, on the other hand, providingguidance with respect to the engine block of the transmission membersecured to the piston using a synchronized rolling guide device.

The mechanical transmission device according to the present invention isdesigned to reduce vertical bulk.

The mechanical transmission device according to the present inventionhas the advantage of making it easier to machine each component of thevariable cylinder capacity engine.

The mechanical transmission device for a variable cylinder capacityengine according to the present invention comprises at least onecylinder in which a piston moves. The piston is secured at its lowerpart to a transmission member and collaborates with a small-sized rackwith a rolling guide device and a first large-sized rack, with a toothedwheel connected to a connecting rod. The device also includes a controlmember comprising a second large-sized rack collaborating with thetoothed wheel and fixing means for fixing the piston onto thetransmission member. The fixing means preload clamps and centers thepiston. The device further includes connecting means which stiffen thetransmission and/or control members and increase the bending strength ofthe teeth of the large-sized racks. The device still further includeslightening means for lightening the toothed wheel and which preserve therigidity of the toothed wheel. The lightening means also preserves theability of the toothed wheel to transmit force.

The mechanical transmission device according to the present inventioncomprises means for guiding the piston which consist, at the cylinder ofa short guide skirt secured to the piston and, at the transmissionmember, of a rolling guide device which comprises a single synchronizedroller.

The mechanical transmission device according to the present inventioncomprises means for fixing the piston onto the transmission member. Themeans for fixing consist of a threaded bore produced in a supporting legof the piston and of a vertical threaded rod secured to the transmissionmember. The vertical threaded rod collaborates with the threaded bore tofix the piston onto the transmission member in a preloaded manner.

The mechanical transmission device according to the present inventioncomprises a piston having a threaded bore. The threaded bore is a plaincoaxial bore collaborating with a plain portion provided on the verticalrod of the transmission member so as to center the piston as the pistonis fixed onto the transmission member.

The mechanical transmission device according to the present inventioncomprises a piston having a supporting leg. The supporting leg has, inits internal part, a threaded bore communicating with radial openingswhich open into the upper part of the supporting leg.

The mechanical transmission device according to the present inventioncomprises a piston having radial openings open between fins provided onthe external periphery of the supporting leg.

The mechanical transmission device according to the present inventioncomprises a piston having, between the guide skirt and a piston ringgroove, ducts which open between the fins of the supporting leg.

The mechanical transmission device according to the present inventioncomprises connecting means connecting the teeth of the large-sized rackof the transmission member. The connecting means consist of lateralcheeks stiffening the transmission member and increasing the bendingstrength of the teeth of the large-sized rack.

The mechanical transmission device according to the present inventioncomprises a transmission member having lateral cheeks that can be usedas runway tracks collaborating with runway tracks positioned laterallyon the toothed wheel.

The mechanical transmission device according to the present inventioncomprises connecting means connecting the teeth of the large-sized rackof the control member. The connecting means consist of lateral cheeksstiffening the control member and increasing the bending strength of theteeth of the large-sized rack.

The mechanical transmission device according to the present inventioncomprises a control member having lateral cheeks that can be used asrunway tracks collaborating with runway tracks positioned laterally onthe toothed wheel.

The mechanical transmission device according to the present inventioncomprises transmission and control members in which the large-sizedracks comprise lateral cheeks. The lateral cheeks are formed bymachining and/or forging the bodies that make up said transmission andcontrol members.

The mechanical transmission device according to the present inventioncomprises transmission and control members in which the large-sizedracks comprise lateral cheeks which are added onto and fixed to bodiesthat make up said transmission and control members.

The mechanical transmission device according to the present inventioncomprises a toothed wheel having a cutout on its upper profile so as toreduce the vertical bulk of the engine.

The mechanical transmission device according to the present inventioncomprises a toothed wheel which is made up of two toothed half-wheelsjoined together.

The mechanical transmission device according to the present inventioncomprises a toothed wheel which is made up of two toothed half-wheelsjoined together exhibiting a cutout on their upper profile so as toreduce the vertical bulk of the engine.

The mechanical transmission device according to the present inventioncomprises lightening means for lightening the toothed wheel, whichconsist of at least one cavity.

The mechanical transmission device according to the present inventioncomprises a toothed wheel and large-sized racks belonging to thetransmission and control members, the teeth of which have differentwidths.

The mechanical transmission device according to the present inventioncomprises a toothed wheel and large-sized racks belonging to thetransmission and control members, the teeth of which are of differentdimensions.

The mechanical transmission device according to the present inventioncomprises a toothed wheel and large-sized racks belonging to thetransmission and control members, the teeth of which have differentprofiles.

The mechanical transmission device according to the present inventioncomprises a toothed wheel the teeth of which exhibit impressions ontheir lateral faces which determine the stiffness of the edge of theseteeth.

The mechanical transmission device according to the present inventioncomprises a toothed wheel. A central cavity of the toothed wheel hasinternal faces that act as guide surfaces for the lateral guidance ofthe small end of the connecting rod.

The mechanical transmission device according to the present inventionwherein each toothed half-wheel has internal faces that act as a guidesurface for the lateral guidance of the small end of the connecting rod.

The mechanical transmission device according to the present inventioncomprises a toothed wheel having a pivot axis. The pivot axis issituated in a bore of the toothed wheel and is offset from the center ofthe pitch circle of the toothed wheel so as to obtain variations in thekinematics of the piston.

The mechanical transmission device according to the present inventionwherein the threaded rod of the transmission member has at its middle, ahole which opens, on the one hand, above a runway track of thetransmission member and, on the other hand, into the threaded boreformed in the supporting leg of the piston.

The mechanical transmission device according to the present inventioncomprises transmission and control members having runway tracks whichare produced by machining and/or forging the bodies of said transmissionand control members.

The mechanical transmission device according to the present inventioncomprises a transmission member which is provided with lightening means.

The mechanical transmission device according to the present inventioncomprises a rolling guide device which is made up of a synchronizedroller and of a small-sized rack device secured to the engine block. Therolling guide device collaborates with the small-sized rack of thetransmission member so as to guide the transmission member on the engineblock and to synchronize the vertical movement of said roller withrespect to the piston.

The mechanical transmission device according to the present inventioncomprises a rolling guide device having a roller that consists of acylindrical body comprising, at each end, pinions and an axial guidegroove provided between the pinions.

The mechanical transmission device according to the present inventioncomprises a rack device secured to the engine block. The rack device hasa central body forming a runway track. The runway track has, at itsmiddle, a vertical rib which collaborates with the guide groove of theroller so as to provide lateral guidance therefor. The rack device alsohas racks which are fixed onto the vertical edges of said body tocollaborate with the pinions of the roller so as to synchronize thevertical movement of said roller with that of the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

The description which will follow with reference to the appendeddrawings, given by way of nonlimiting examples, will allow for a betterunderstanding of the invention, of the features it offers and of theadvantages it is able to afford:

FIG. 1 is a perspective view illustrating all of the components thatmake up the mechanical transmission device according to the presentinvention.

FIG. 2 is an exploded perspective view depicting the mechanicaltransmission device according to the present invention.

FIGS. 3 to 8 are views depicting in detail the piston of the mechanicaltransmission device according to the present invention.

FIGS. 9 to 13 are views illustrating in detail the transmission membersecured to the piston of the mechanical transmission device according tothe present invention.

FIG. 14 is a perspective view showing in detail part of the rollingguide device according to the present invention.

FIGS. 15 to 18 are views depicting a toothed wheel of the mechanicaltransmission device according to the present invention.

FIG. 19 is a perspective view showing in detail the control membercollaborating with a toothed wheel of the mechanical transmission deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 depict a mechanical transmission device 1 for a variablecylinder capacity engine comprising a piston 2 which is guided anddriven in translational movement in a cylinder 10 of the engine block.

The piston 2 is secured at its lower part to a transmission member 3which collaborates with a rolling guide device 4 and with a toothedwheel 5.

The toothed wheel 5 transmits the motion between a crankshaft 9 and thetransmission member 3 secured to the piston 2 via a connecting rod 6 onwhich the toothed wheel 5 is mounted, by means of a connecting pin 61which allows the toothed wheel 5 to pivot.

The toothed wheel 5 collaborates at the opposite end of the transmissionmember 3 with another member known as the control member 7 which ismounted in a recess or on a guide which are formed in the engine block.

The position of the control member 7 with respect to the engine block isafforded by a positioning device, not depicted, but described in aFrench patent application No 98 04601 belonging to the Applicant.

FIGS. 3 to 8 show the piston 2 which is made up of a thick disk 20provided with the grooves able respectively to receive the firing ring,compression ring and oil-control ring all known per se.

The disk 20 comprises, in its lower part, a short guide skirt 21 whichguides the piston 2 in the cylinder 10.

The underside of the thick disk 20 is secured to a supporting leg 22bearing fins 23 on an external periphery of the supporting leg.

The supporting leg 22 comprises, in its internal part, a bore 24 whichopens into radial openings 25 formed in the upper part of saidsupporting leg.

The radial openings 25 open between the fins 23 of the supporting leg22.

Between the guide skirt 21 and a piston ring groove 27 the piston 2comprises ducts 26 which open between the fins 23 of the supporting leg22.

The bore 24 exhibits, at the base of the supporting leg 22, a threadedpart 28 and a plain coaxial centering bore 29.

The supporting leg 22 comprises, on its external periphery andunderneath the fins 23, at least one purchase for a tool to turn thepiston 2 when the piston is being fixed onto the transmission member 3.The at least one purchase, for example, takes the form of twodiametrically opposed impressions 8.

The piston 2 can be fixed in its unfinished state onto the controlmember 3 and then machined to form all of the surfaces, particularlythose which have a functional surface finish.

FIGS. 9 to 13 depict the transmission member 3 which in one embodimentis a 1-piece body 30. The body 30 has at an upper part, a threaded rod31 extending vertically and collaborating with the threaded part 28 ofthe bore 24 when the piston 2 is attached.

The threaded rod 31 comprises a plain portion 32 which collaborates withthe plain coaxial bore 29 of the threaded bore 24 to center the piston 2on the transmission member 3.

The transmission member 3 comprises a large-sized rack 35 which is madeup of parallel teeth 34 and a runway track 36 which is set back from thecrests of said teeth and lies near the pitch circle of the large-sizedrack 35.

The parallel teeth 34 of the large-sized rack 35 are verticallyseparated by the runway track 36.

The transmission member 3 comprises connecting means connecting theteeth 34 of the large-sized rack 35. The connecting means may be lateralcheeks 11 and 12 that stiffen the transmission member 3 and increasingthe bending strength of the teeth 34 of the large-sized rack 35.

The lateral cheeks 11, 12 and the runway track 36 are produced bymachining and/or forging the body 30 of the transmission member 3.

The lateral cheeks 11 and 12 may also be added onto and fixed to thebody 30 of the transmission member 3.

Alternatively, the lateral cheeks 11 and 12 may be used as a runwaytrack collaborating with runway tracks positioned laterally on thetoothed wheel 5. In this case, the runway track 36 may be omitted.

The threaded rod 31 comprises, at its middle, a hole 33 which opens intothe bore 24 of the piston 2 and above the runway track 36 separating theteeth 34 of the large-sized rack 35.

The hole 33, when the engine is running, plays a part in lubricating therunway track 36 because the hole communicates directly with the internalbore 24 of the piston 2 which, via the radial openings 25, receives oilfrom the lower part of the engine.

What really happens is that the engine lubricating oil is injected bynozzles, not depicted, or splashed onto the underside of the piston 2.

Thus, the oil circulates within the bore 24 of the piston 2 and betweenthe fins 23 via the radial openings 25.

The transmission member 3 comprises, at the opposite end to thelarge-sized rack 35 and on one of the vertical edges 39 of thetransmission member, another, small-sized rack 37 and a runway track 38which collaborate with the rolling guide device 4 secured to the engineblock.

The small-sized rack 37 may be machined directly into the body 30 oradded onto and fixed to the body 30. The rack 37 may be equally providedon each of the vertical edges 39 of the body 30, depending on theconstruction of the rolling guide device 4.

The body 30 of the transmission member 3 is provided with a lighteningmeans which, for example, consist of a series of blind lightening holes13.

FIGS. 2 and 14 illustrate the rolling guide device 4 which consists of asynchronized roller 40 and of a rack device 41 secured to the engineblock. The rolling guide device 4 guides the transmission member 3 onthe engine block and synchronizes the vertical movement of said roller40 with respect to the piston 2.

The roller 40 is made up of a cylindrical body 42 comprising pinions 44at each end.

The cylindrical body 42 at its middle and between the pinions 44 has aguide groove 43.

The rack device 41 is made up of a central body 45 and of racks 46 whichare fixed to the vertical edges 47 of said body 45. The body 45comprises a runway track 48 and a vertical rib 49.

The first pinion 44 of the roller 40 collaborates with the small-sizedrack 37 of the transmission member 3 and with one of the racks 46 of therack device 41.

The second pinion 44 of the roller 40 collaborates only with the otherrack 46 of the device 41, while the vertical rib 49 of the body 45collaborates with the guide groove 43 of the body 42 to provide lateralguidance for the roller 40.

The body 42 of the roller 40 provides guidance for the transmissionmember 3 by rolling along the runway track 38 of said member and byrolling along the track 48 of the body 45 of the rack device 41.

FIGS. 1, 15 and 16 depict the toothed wheel 5 of the mechanicaltransmission device 1 according to the present invention.

The toothed wheel 5 is made up of two toothed half-wheels A and B whichare joined together, for example, by welding, brazing, electron welding,laser welding or electromagnetic induction brazing.

The toothed wheel 5, which may or may not be made up of two toothedhalf-wheels A and B, has a cutout 16 on its upper profile 59 to reducethe vertical bulk of the transmission device according to the inventionas a whole.

The toothed wheel 5 also has a central cavity 53 into which there opensa bore 50 for the placement of the small end 60 of the connecting rod 6via the connecting pin 61.

The internal faces of the central cavity 53 of the toothed wheel 5 haveguide surfaces 14 for laterally guiding the small end 60 of theconnecting rod 6.

Also, the internal faces of each toothed half-wheel A and B of thetoothed wheel 5 exhibit a guide surface 14 for the lateral guidance ofthe small end 60 of the connecting rod 6.

The toothed wheel 5 comprises a first set of teeth 51 collaborating withthe teeth 34 of the large-sized rack 35 of the transmission member 3secured to the piston 2 and a second set of teeth 52 collaborating withthe large-sized rack 73 of the control member 7.

Each set of teeth 51, 52 comprises at its middle a groove 54 coaxialwith the pitch circle of the toothed wheel 5.

Within each groove 54 is fixed a runway strip 55 exhibiting a curvedprofile similar to that of said groove. Each runway strip 55 is fixed,for example by laser welding or electron welding, into the correspondingcurved groove 54.

The toothed wheel 5 has cavities 56 which may or may not be blind in thecentral cavity 53. The cavities 56 are designed to lighten the toothedwheel 5 while at the same time preserving its rigidity and itsload-bearing capacity.

The cavities 56 may be separated from one another by thin webs 57 so asto stiffen the structure of the toothed wheel 5.

The set of teeth 51 comprises in its upper part teeth 58 of a width thatis reduced by comparison with the other teeth of the toothed wheel 5.

The upper cutout 16 of the toothed wheel 5 and the teeth 58 make itpossible to reduce the vertical bulk of the mechanical transmissiondevice 1.

This is because, with this configuration, the teeth 58 penetrate furtherinside the cylinder 10 when the piston 2 is near the top of its stroke.

Also, the set of teeth 52 comprises, in its lower part, teeth 58 of awidth which is reduced by comparison with the other teeth so as to bringthe center of gravity of the toothed wheel 5 closer to its pivot axis.

The pivot axis of the toothed wheel 5, which axis is situated in thebore 50, may be offset from the center of the pitch circle of saidtoothed wheel. The offsetting of the pivot axis of the toothed wheel 5makes it possible to obtain variations in the kinematics of the piston2.

FIGS. 17 and 18 depict the toothed wheel 5 provided with means formastering the edge effect of the sets of teeth.

It is known that in order to avoid excessive stress on the edges of thesets of teeth the teeth may be corrected in a way currently termed“curving”.

This operation which is expensive in industry may be replaced by controlover the stiffness of the teeth of the toothed wheel 5 across theirwidth, and particularly on the edges of said teeth.

This control, which is the subject of the present invention, will beobtained by making at least one impression 15 on each side of the teethof the toothed wheel 5.

These impressions 15 have shapes such that they reduce the stiffness ofthe edges of the teeth of the toothed wheel 5 so as to limit thestresses due to the edge effect.

These impressions 15 may be produced when the toothed wheel 5 is beingforged.

FIG. 19 shows the control member 7 which comprises a large-sized rack 73and a vertical runway track 70 with which the runway strip 55 providedat the middle of the set of teeth 52 of the toothed wheel 5collaborates.

The parallel teeth 74 of the large-sized rack 73 are verticallyseparated by the runway track 70.

The control member 7 comprises connecting means connecting the teeth 74of the large-sized rack 73 which consist of lateral cheeks 71 and 72stiffening the control member 7 and increasing the bending strength ofthe teeth of the large-sized rack 73.

The lateral cheeks 71, 72 and the runway track 70 are produced bymachining and/or forging the body of which the control member 7 is made.

Provision may be made for the lateral cheeks 71 and 72 to be added ontoand fixed to the body of the control member 7.

By way of an alternative, the lateral cheeks 71 and 72 may be used as arunway track collaborating with runway tracks positioned laterally onthe toothed wheel 5. In this case, the runway track 70 may be omitted.

It must also be understood that the foregoing description has been givenmerely by way of example and that it does not in any way restrict thescope of the invention which would not be exceeded if embodiment detailsdescribed were replaced by any other equivalent.

1. A mechanical transmission device for a variable cylinder capacityengine comprising: at least one cylinder; a transmission member; apiston movable within said cylinder, said piston being secured at alower part to said transmission member, said transmission member havinga first small-sized rack that collaborates with a rolling guide deviceand a first large-sized rack that collaborates with a toothed wheel,said toothed wheel being connected to a connecting rod; a control membercomprising a second large-sized rack collaborating with the toothedwheel; fixing means for fixing the piston onto the transmission member,said fixing means provide clamping preload and center the piston;connecting means that stiffen at least one of the transmission and thecontrol member and that increase the bending strength of the teeth ofthe first and second large-sized racks; and lightening means forlightening the toothed wheel while preserving the rigidity and theload-bearing capacity of the toothed wheel.
 2. The mechanicaltransmission device as claimed in claim 1, further comprising means forguiding the piston, said means for guiding comprise, at the cylinder, ashort guide skirt secured to the piston and, at the transmission member,said rolling guide device, said rolling guide device comprising a singleroller.
 3. The mechanical transmission device as claimed in claim 2,wherein the piston comprises ducts, between the guide skirt and a pistonring groove, said ducts open between fins on an external periphery ofthe supporting leg.
 4. The mechanical transmission device as claimed inclaim 1, wherein the means for fixing the piston onto the transmissionmember comprises a threaded bore produced in a supporting leg of thepiston and a vertical threaded rod secured to the transmission member,which collaborates with the threaded bore to clamp the piston onto thetransmission member.
 5. The mechanical transmission device as claimed inclaim 4, wherein the threaded bore comprises a plain coaxial borecollaborating with a plain portion provided on the vertical rod of thetransmission member so as to center the piston as the piston is fixedonto the transmission member.
 6. The mechanical transmission device asclaimed in claim 4, wherein the threaded bore is in an internal part ofsaid supporting leg and communicates with radial openings which openinto an upper part of said supporting leg.
 7. The mechanicaltransmission device as claimed in claim 6, wherein the radial openingsin the piston open between fins provided on an external periphery of thesupporting leg.
 8. The mechanical transmission device as claimed inclaim 6, wherein internal faces of each toothed half-wheel has a guidesurface for laterally guiding a small end of the connecting rod.
 9. Themechanical transmission device as claimed in claim 1, wherein theconnecting means connect the teeth of the first large-sized rack of thetransmission member, said connecting means comprise lateral cheeksstiffening the transmission member and increasing the bending strengthof the teeth of the first large-sized rack.
 10. The mechanicaltransmission device as claimed in claim 9, wherein the lateral cheekscan be used as runway tracks collaborating with runway tracks positionedlaterally on the toothed wheel.
 11. The mechanical transmission deviceas claimed in claim 10, wherein the lateral cheeks can be used as runwaytracks collaborating with runway tracks positioned laterally on thetoothed wheel.
 12. The mechanical transmission device as claimed inclaim 9, wherein the first and second large-sized racks comprise lateralcheeks which are produced by machining and/or forging the bodies thatmake up said transmission and control members.
 13. The mechanicaltransmission device as claimed in claim 9, wherein the large-sized rackscomprise lateral cheeks which are added onto and fixed to bodies thatmake up said transmission and control members.
 14. The mechanicaltransmission device as claimed in claim 1, wherein the connecting meansconnect the teeth of the second large-sized rack of the control member,said connecting means comprise lateral cheeks stiffening the controlmember and increasing the bending strength of the teeth of the secondlarge-sized rack.
 15. The mechanical transmission device as claimed inclaim 1, wherein the toothed wheel has a cutout on an upper profile soas to reduce the vertical bulk of the engine.
 16. The mechanicaltransmission device as claimed in claim 15, wherein the toothed wheelcomprises a central cavity having internal faces with guide surfaces forlaterally guiding a small end of the connecting rod.
 17. The mechanicaltransmission device as claimed in claim 15, wherein the toothed wheelhas a pivot axis situated in a bore which is offset from the center ofthe pitch circle of said toothed wheel so as to obtain variations in thekinematics of the piston.
 18. The mechanical transmission device asclaimed in claim 1, wherein the toothed wheel is made up of two toothedhalf-wheels joined together.
 19. The mechanical transmission device asclaimed in claim 18, wherein the two toothed half-wheels each have acutout on their upper profile so as to reduce the vertical bulk of theengine.
 20. The mechanical transmission device as claimed in claim 1,wherein the lightening means for lightening the toothed wheel comprisesat least one cavity.
 21. The mechanical transmission device as claimedin claim 1, wherein teeth of the first and second large-sized racks havedifferent widths.
 22. The mechanical transmission device as claimed inclaim 1, wherein teeth of the first and second large-sized racks are ofdifferent dimensions.
 23. The mechanical transmission device as claimedin claim 1, wherein teeth of the first and second large-sized racks havedifferent profiles.
 24. The mechanical transmission device as claimed inclaim 1, wherein teeth of the toothed wheel have impressions on theirlateral faces which determine the stiffness of the edge of said teeth.25. The mechanical transmission device as claimed in claim 1, whereinthe transmission member has a threaded rod that has at its middle, ahole which opens above a runway track of the transmission member andinto a threaded bore formed in a supporting leg of the piston.
 26. Themechanical transmission device as claimed in claim 1, wherein thetransmission and the control members comprise runway tracks which areproduced by machining the bodies that make up said transmission andcontrol members.
 27. The mechanical transmission device as claimed inclaim 1, wherein the transmission member is provided with lighteningmeans.
 28. The mechanical transmission device as claimed in claim 1,wherein the rolling guide device comprises a synchronized roller and asecond small-sized rack device secured to the engine block whichcollaborates with the first small-sized rack of the transmission memberso as to guide the transmission member on the engine block and tosynchronize the vertical movement of said roller with respect to thepiston.
 29. The mechanical transmission device as claimed in claim 28,wherein the roller has a cylindrical body comprising, at each end,pinions and a guide groove provided between the pinions.
 30. Themechanical transmission device as claimed in claim 28, wherein thesecond small-sized rack device comprises a central body forming a runwaytrack comprising, at its middle, a vertical rib which collaborates witha guide groove of the roller so as to provide lateral guidance therefor,and third small-sized racks which are fixed onto the vertical edges ofsaid central body to collaborate with the pinions of the roller so as tosynchronize the vertical movement of said roller with that of thepiston.